The increase in the degree of integration of LSIs used in computers or the like is being accelerated by generation and generation. This accelerated increase in the degree of integration has caused a trend of increase in the amount of generated heat. In order to allow an LSI to operate rapidly and stably, the operating temperature of the LSI must be controlled to ascertain level or lower. Therefore, there is generally used a cooling device according to an amount of heat that the LSI generates.
For example, Japanese Laid-Open Patent Publication No. H08-255855 proposes an air-cooling module structure in which a heat sink is attached on an LSI and a fan is arranged over the heat sink to apply cool air thereto. Additionally, Japanese Laid-Open Patent Publication No. 2006-100692 proposes a liquid-cooling module in which a heat receiving portion, a pump, a radiator, and a reserve tank are disposed above an LSI to circulate liquid.
The air-cooling module structure as described in No. H08-255855 has a problem that it is difficult to cool an LSI generating a large amount of heat. The heat sink is made of a metal such as copper or aluminum having high heat conductivity. Heat generated by the LSI is diffused, by heat conduction, from a contact portion with the heat sink to the whole heat sink, and then discharged to the outside air from fins on the surface of the heat sink. The capacity to conduct the heat from the contact portion with the LSI to the fins drops as the amount of generated heat is increased. In this state, the cooling capacity will not be improved significantly even if the size of the heat sink is increased. Although the cooling capacity may be improved by increasing the rotation speed of the fan, this will cause a problem of noises. In general, when the rotation speed of the fan is doubled, the acoustic pressure will also be increased by 15 to 18 dB.
On the other hand, the liquid-cooling module may solve this problem, but, at the same time, a radiator is additionally required to cool the liquid coolant circulating system including a pump and pipes, as well as the liquid coolant which has received heat from the LSI.
The liquid-cooling module according to Japanese Laid-Open Patent. Publication No. 2006-100692 has a structure, as shown in FIG. 2 of the publication, in which a heat receiving portion, a pump, a reserve tank, and a radiator are stacked on top of an LSI. The projection area occupied by the liquid-cooling module is greater than the LSI packaging area, and hence the board area around the LSI is also covered with the liquid-cooling module. This limits the sizes of other components mountable on the board area around the LSI to be cooled. Components which can be mounted on the covered board area must have a size that is small enough to fit in the gap between the board and the lower surface of the liquid-cooling module. Therefore, only components having a small height can be mounted, or no other components can be mounted around the LSI. Even if there can be provided enough space to mount the components, the space around the components will be so small that the air flow tends to be impeded. This restricts the mounting of heat generators.
Further, the liquid-cooling module according to Japanese Laid-Open Patent Publication No. 2006-100692 has difficulty to maintain stable contact between the LSI and the heat receiving portion, posing a problem in maintaining the cooling efficiency. The liquid-cooling module has a greater number of components and a greater weight than an air-cooling module. This is because the liquid-cooling module includes not only a radiator as an alternative of the heat sink of the air-cooling module but also a heat receiving portion made of copper or the like, a pump, a reserve tank, and liquid coolant, and the weights of these components are added. However, the liquid-cooling module according to Japanese Laid-Open Patent Publication No. 2006-100692 is fixed to the board at its contact portion with the LSI. When the entire apparatus including the liquid-cooling module is moved, the liquid-cooling module having a great weight will oscillate around a fulcrum on the LSI. As a result, the contact between the LSI and the heat receiving portion becomes instable and the cooling efficiency drops. If the oscillation is large, the LSI may be broken. Particularly, when a board is set upright as shown in FIG. 13, moment force will be generated even while the liquid-cooling module is at standstill, and hence the contact portion between the LSI and the heat receiving portion will be constantly subjected to a force that acts to separate the LSI and the heat receiving portion, contributing to deterioration of stability in contact between them and hence deterioration of cooling efficiency.